In the semiconductor device manufacture industry, a dedicated scanning electron microscope called critical dimension—scanning electron microscope (CD-SEM) is widely used to measure dimensions of fine circuit patterns formed on a sample. Furthermore, in forming a circuit pattern on a wafer, a technique of transferring a pattern of an opaque film formed on a transparent substrate called photomask by using short wavelength laser light having a wavelength of approximately 200 nm forms a mainstream. Measurement of dimensions of a pattern on a photomask is also an important quality control process.
If the balance between an electron beam incident on a sample and secondary electrons emitted from the sample by irradiation with the electron beam is zero, the sample is not charged. However, a secondary electron emission efficiency δ (=emitted electron quantity/incident electron quantity) which indicates a ratio of incident electrons to emitted electrons changes according to landing energy at the time when the electron beam is incident on the sample. If landing energy which makes the secondary electron emission efficiency equal to unity us selected according to the kind of the sample, therefore, sample charging is not caused theoretically. As a matter of fact, however, the landing energy is sometimes determined according to the measurement or inspection conditions or the like. In some cases, therefore, condition setting with only the balance of electrons taken into consideration cannot be conducted. In Patent Document 1, a technique of repelling secondary electrons by a potential barrier generated by irradiation with the electron beam and thereby relaxing the positive charging generated in the sample is described. Especially in the Patent Document 1, it is described to control a voltage applied to an electrode which is disposed to be opposed to a sample in order to stabilize the charging.